Method for treating acrylic composite fiber



United States Patent 41/ 82,290 US. Cl. 264-168 Int. Cl. D02g 1/00 6 Claims ABSTRACT OF THE DISCLOSURE Acrylic composite fiber which is produced and used in the manner known in the art for this type of fiber is improved for its intended purposes by a modification according to which the relaxation heat treatment is carried out by immersing the stretched fiber, while it is in such a state that its moisture content is'at least 20 percent relative to the dry weight of the fiber, in an organic liquid medium which does not dissolve the fiber at a temperature of at least 105 C. and is immiscible with water, thereby not only subjecting the fiber to a relaxing heattreatment but also simultaneously causing a three-dimensional coil crimp to be developed in said fiber.

This invention relates to a method of relaxing acrylic composite fiber and, more particularly, to a method for carrying out a relaxing heat-treatment of an acrylic composite fiber consisting of acrylic polymers having dissimilar thermal behaviors arranged in eccentric or laminar relation throughout the length of fiber, characterized in that the fiber, in moistened state, is heat-relaxed in a hot organic medium in which said fiber is not soluble and which is not miscible with water, whereby a uniform threedimensional coil crimp is simultaneously developed in the fiber.

It is well known in the art that when an acrylic composite fiber is subjected to a heat-treatment in a relaxed state, a three-dimensional coil crimp is produced. It is also known that a relaxed heat-treatment of synthetic fiber may be conducted in hot water, pressurized steam, molten salts, molten metals and the like. However, when this heattreatment is carried out in hot water, it is impossible to employ a temperature above 100 C. at atmospheric pressure. Therefore, there is not obtainable sufficient eifect of relaxation when an acrylic synthetic fiber is subjected to a heat-treatment in a relaxed state in hot water under atmospheric condition, and as a result, physical characteristics, particularly knot strength or anti-fibrillation of the fiber is considerably low. Further, it is not possible to produce a sufiiciently developed three-dimensional coil crimp in case of an acrylic composite fiber.

In the case of a continuous relaxing heat-treatment with pressurized water vapor, it is necessary to provide pressure-sealing means at the fiber feed-in zone and takeout zone of the heat-trea ing apparatus (refer forexample to US. Patent No. 3,041,863. For this purpose, various proposals have been made, but especially when the crimped fiber bundle is continuously withdrawn at the take-out zone of the apparatus, the frictional resistance created between the pressure-sealing means and fiber bundle causes a partial loss of the three-dimensional coil crimp which has been developed by said relaxing heat treatment, with the result that it is impossible to obtain a uniform three-dimensional coil crimp in the final fibers.

Furthermore, there has also been proposed a relaxing heat-treatment using a molten metal, as well as a relaxing heat-treatment involving the use of a molten salt. However, these techniques involve the relaxing heat-treatment by passing the fiber through a molten mass of metal or salt, and accordingly both of the techniques not only tend to cause an extensive damage to the fiber, but do not allow a three-dimensional crimp to be fully developed because of the high viscosity of the molten mass.

The present invention has as its object to provide an improved method whereby an acrylic composite fiber is not only relaxed but also is simultaneously endowed with a stabilized, uniform three-dimensional crimp.

The above-mentioned object is accomplished according to this invention by a method which comprises spinning conjugatedly two dissimilar acrylic composite fiber in which said polymers are arranged eccentrically or in laminar relation throughout the length, stretching the composite fiber and then subjecting the fiber to a relaxation heat-treatment, characterized in that the relaxation heat-treatment is conducted by immersing the fiber, in such a state as containing at least 20% of water based on the dry weight of the fiber, in an organic heating medium maintained at a temperature of at least C.

Since the acrylic composite fiber of this kind and its production in general (spinning, stretching, etc.) are well known in the art and do not constitute a novel feature of the invention, no detailed explanation thereabout will be required, except the particular relaxation heat-treatment which is the very subject of this invention.

The important point in the relaxation heat-treatment of the invention is that the water content of the fiber to be immersed in the organic heating medium must be at least 20 percent or higher with respect to the dry weight of the fiber. Should the water content of fiber be less than 20 percent, the three-dimensional crimp could not be developed to a satisfactory degree on relaxing heattreatment in the heating medium.

While there is no critical upper limit in the Water content, it is usually up to 400% based on the dry weight of the fiber.

The temperature of the organic heating medium wherein the relaxation heat-treatment is conducted must be at least 105 C. In case the temperature is below 105 C., it is impossible to attain a satisfactory relaxing effect, nor is it possible to develop the desired three-dimensional coil crimp. As the temperature of the organic heating medium increases, the effect of the relaxing treatment is accordingly enhanced, and, at the same time, the three-dimensional crimp is developed to a greater degree, but if excessively high temperatures are employed, the treated fiber will be considerably discolored. For this reason, the preferred temperature range for said treatment with an organic heating medium is from 105 C. to C.

While it varies somewhat with the temperature of the organic heating medium and the water content of the fiber, the time required before both a satisfactory relaxing effect and a full development of the three-dimensional crimp are attained in said organic heating medium is usually 30 seconds to 3 minutes.

(The organic heating medium which is employed according to this invention must be a liquid organic compound which does not dissolve acrylic synthetic fiber at temperatures above 105 C. and which is not miscible with water. Thus, in an organic heating medium immiscible with water, the water contained in the fiber is rapidly converted to vapor, which causes a thermal shrinkage of the fiber while plasticizing the same. Moreover, as the wa-ter is evaporated, the fiber bundle is caused to ravel into monofilaments, thereby weakening the bondage between the individual filaments, and accordingly, facilitating the development of the desired three-dimensional coil crimp.

In contrast, when a water-miscible organic heating medium is employed, the water contained in the fiber dissolves itself into the organic medium when the fiber is immersed therein, with the result that the amount of water vapor generated around the fiber is lowered. This reduction in amount of the water vapor not only detracts from the plasticizing effect of the vapor on the fiber but also brings about a considerable decrease in the raveling elfect explained above. The net result is that the threedimensional coil crimp is considerably degraded.

Typical examples of the above-mentioned organic compound to be used in the invention include mineral oil, vegetable oils, silicone oils, etc. having a boiling point of at least 105 C. at atmospheric pressure but in order to meet the requirements that they are chemically stable at high temperatures and that the three-dimensional coil crimp can be more easily developed, it is necessary that the compound should have a sufficiently low viscosity. in this respect, liquid paratfin, kerosine, spin-dle oil, etc. are particularly preferred as mineral oils. Prefer-able examples of vegetable oils are cotton seed oil, coconut oil, soybean oil and peanut oil.

T he acrylic composite fiber to be employed according to this invention may be one which has been prepared either by dry-spinning or by wet-spinning, and the invention may be applied irrespective of whether the fiber is in the form of filament or of tow. The present invention is also applicable irrespective of whether the fiber is one (from the hot-humid stretching process and accordingly containing at least 20 percent of water relative to the dry weight of the fiber or it is an unrelaxed composite fiber which has been provided with at least 20 percent of water through sprinkling of water or by passage through a water bath.

Acrylic polymers constituting composite fibers include not only polyacrylonitrile but also acrylonitrile copolymers which contain at least 80% by weight of acrylonitrile and also include a blend of two or more of these polymers. Comonomers to be copolymerized with acrylonitrile to form the copolymers include methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, met-hoxyethyl acrylate, phenyl acrylate, cyclohexyl acrylate, dimethylaminoethyl acrylate and corresponding methylacrylates; alkl substituted products and nitrogen substituted products of acrylamides and methac-rylamides; unsaturated ketones such as methyl vinyl ketone, phenyl vinyl ketone, methyl isopropenyl ketone, etc.; vinyl carboxylates such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc.; esters of ethylene alpha and beta carboxylic acids such as fumaric acid, citraconic acid, mesaconic acid, aconic acid, etc.; N-alkyl-maleinimide; N- viny'l carbazol; N-vinyl succinimide; N-vinyl phthalimide; vinyl etheis; N-methylolacrylamide; vinyl pyridines such as 2-vinyl pyridine, 4-vinyl pyridine and 2-methyl-5-vinyl pyridine; styrene and its alkyl substituted products; allyl alcohol; vinyl chloride; vinylidene chloride; vinylidene cyanides; unsaturated organic sulfonic acids such as allyl sulfonic acid, methallyl sulfonic acid, allyoxyethyl sulfonic acid, methal-lyloxyethyl sulfonic acid, allyl-thioethyl sulfonic acid, allylthiopropanol sulfonic acid, isopropenylbenzene sulfonic acid, vinyl bnomobenzene sulfonic acid,

vinyl fluorobenzene sulfonic acid, styrene sulfonic acid, methyl styrene sulfonic acid, etc. and their water soluble salts.

As explained before, the relaxation heat treatment of this invention is conducted after the composite fiber has been spun and stretched. The stretching of the composite fiber may be conducted in a well known manner. Thus, the swollen gel composite fiber emerging from the coagulating bath is washed with water, and then, stretched 3-20 times the initial length, whereby the fiber assumes the practical degree of strength and elongation. T he stretching may be carried out in one step, but by taking advantage of the cold-stretchability of the unstretche-d fiber, it is possible to stretch the fiber 1.1-4 times in the washing water bath at room temperature and, then, hot stretch the same so that the total stretch ratio would be 3-20 times the initial length. It is also possible to carry out a hot-stretching of the fiber in several steps. The hot-stretching may also be carried out in steam at l00-140 C.

The following examples are shown to illustrate the invention and not to limit the scope of the invention. In these examples, all parts and percentages are by weight unless otherwise specified.

Example 1 A copolymer consisting of 91 parts of acrylonitrile 9 parts of methyl acrylate and 0.5 part of sodium methallyl sulfonate and other copolymer consisting of 88.5 parts'of acrylonitrile, 11.5 parts of methyl acrylate and 0.5 parts of sodium methallylsulfonate were dissolved respectively in 49% aqueous solutions of sodium thiocyanate to prepare spinning solutions respectively containing 10% of the copolymers. By means of two units of the metering pump and apparatus shown in US. Patent No. 3,182,106, equal amounts of the spinning solutions are conjugatedly extruded through a spinnerette having 60 orifices, each 0.09 mm. in diameter, into an 8% aqueous solution of sodium thiocyanate, and after washing, the resulting tow of composite filaments is stretched ten times the original length in boiling water, followed by drying. The filaments are then continuously passed through a water bath at 40 C., whereby moisture is imparted to the filaments. The water content of the filaments is adjusted by squeezerollers as shown in Table 1. The three filament samples are respectively dipped in liquid parafiin baths respectively heated at C., C. and C. under no tension for 1 minute, to subject the sample to a relaxing heat-treatment, whereupon a three-dimensional coil crimp is produced in the filaments. The filaments are continuously scooped by means of a wire-netting conveyer, on which they are allowed to cool. Then, the filaments are immersed in an aqueous solution of a surface active agent to remove the liquid paraffin, and after washing with water and oiling, the filaments are dried. The results are set forth in Table 1. 1

On the other hand, for comparison purposes, a filament sample is treated in the same manner as above, without imparting moisture to the filaments. Also as a control, a sample is treated in boiling water, in place of liquid parafiin, for 15 minutes. A sample is also treated in liquid paraffin of 100 C. The results are shown in Table 1, wherein the crimp frequency and crimp index are measured as follows:

Crimp frequency: The filaments are loaded with 2 mg. per denier and the number of crimps per 25 mm. is counted. The value is an average of 20 tests.

Crimp index: The filament is loaded with 2 mg. perdenier and the length a is measured. Then the filament is loaded with 50 mg. per denier and the length b is measured after 30 seconds. The crimp index is calculated from the following formula:

Moisture content: Based on the weight of the filament as dried.

TABLE 1 Temp, Moisture Knot Knot Crimp Crimp Uniformity Heating medium C. content strength elongation frequency index of crimps (percent) (g./d.) (percent) Liquid paratfin 25 1. 42 3. 3 12. 3 28. 7 Bad.

D 25 1. 88 5.3 15. 3 33. 8 Good.

' O 1. 71 4. 0 9. 6 14. 3 Bad.

20 2. 9. 2 15.6 32. 7 Good. 25 2.08 7. 9 16. 6 41. 6 D0. 50 2. 21 8. 4 17. 5 44. 6 Do. 100 2. 40 10. 5 20. 4 38. 9 D0. 200 2. 35 11.3 20. 8 37. 1 D0. 400 2. 30 14. 7 17. 8 39. 1 D0. 1. 68 6. 7 13. 7 30. 3 Bad.

It will be apparent from Table 1 that whereas the samples treated by the method of this invention have quite satisfactory properties, the sample treated without the impregnation of Water prior to the relaxing heattreatment, the sample treated in boiling water and the sample treated in liquid paraflin of 100 C. are considerably inferior to the samples of this invention in the development of three-dimensional crimp and, also, in respect to knot strength and knot elongation. Furthermore, there occurs a lack of uniformity of three-dimensional comp.

Example 2 The composite filaments prepared, stretched and dried in the same manner as in Example 1 were continuously passed through a water bath of 45 C. and then rollersqueezed to a moisture content of 50%. The moistened filaments were immersed in a relaxed state in a cotton seed oil bath of 125 C. for 1 minute to conduct a relaxation heat treatment and at the same time to develop coily crimps. The filaments were continuously scooped by a wire-netting conveyor, on which there were allowed to cool. Then the filaments are dipped in an aqueous solution of a surfactant to remove the oil, washed with water, oiled and finally dried. The results are shown in Table 2.

The procedure of Example 2 was repeated except that silicone oil (Toshiba Silicone Oil TS 951-(200), product of Tokyo Shibaura Electric Co., Ltd., of Japan) was employed. The results are shown in Table 3.

TABLE 3 Treating temp. C.)

Moisture content (percent) 5O Knot strength (g./d.) 2.43 Knot elongation (percent) 9.6 Crimp frequency 16.6 Crimp index 43.2

Uniformity of crimps Good What we claim is:

1. A method of treating acrylic composite fiber prepared by extruding two or more acrylic copolymer components having dissimilar thermal behaviors into an acrylic composite fiber in which said components are arranged in eccentric or laminar relation throughout the length of the fiber and stretching the composite fiber, characterized by immersing the stretched fiber, while it is in such a state that its moisture content is at least 20 percent relative to the dry weight of the fiber, in an organic liquid medium which does not dissolve the fiber at a temperature of at least C. and is immiscible with water, thereby not only subjecting the fiber to a relaxing heat-treatment but also simultaneously causing a three-dimensional coil crimp to be developed in said fiber.

2. A method as claimed in claim 1 wherein the organic liquid medium is a mineral oil.

3. A method as claimed in claim 2 wherein the mineral oil is liquid parafiin.

4. A method as claimed in claim 1 wherein the organic liquid medium is a vegetable oil.

5. A method as claimed in claim 4 wherein the vegetable oil is cotton seed oil.

6. A method as claimed in claim 1 wherein the organic liquid medium is silicone oil.

References Cited UNITED STATES PATENTS 3,140,957 7/1964 Tanabe et al.

3,150,223 9/ 1964 Studlik 264-182 X 3,330,896 7/1967 Iujita et al. 264-168 X 2,677,590 5/1954 Hare et a]. 8-1301 2,869,974 1/1959 Adams 8-130.1 3,03 8,236 6/1962 Been 28-82 JULIUS FROM E, Primary Examiner.

I. H. WOO, Assistant Examiner.

US. Cl. X.R. 

